Chemical Tests 2h
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Test for hydrogen
Lit splint goes out with a squeaky pop
Test for oxygen
Glowing splint relights
Test for carbon dioxide
Limewater turns milky/cloudy
Test for ammonia (NH3)
Damp red litmus turns blue
Test for chlorine
Damp blue litmus paper bleaches/turns white
Flame test
Clean platinum wire with concentrated HCl Dip into salt Hold wire into roaring flame
Flame colour for: Lithium, Sodium, Potassium, Calcium, Copper (II)
Lithium: Red Sodium: Orange Potassium: Lilac Calcium: Red Copper (II): Green - Blue
Test for ammonium (NH4)
Red litmus paper & NaOh • Damp red litmus paper turns blue • Add warm NaOH and aluminium as catalyst. Strong odour, gas produced (NH3)
Cu (II) with NaOH
Blue precipitate formed
Fe (II) with NaOH
Green precipitate formed
Fe (III) with NaOH
Brown precipitate formed
Tests for halides
Add nitric acid to remove impurities Add silver nitrate to cause precipitation Chloride: White precipitate Bromide: Cream precipitate Iodide: Yellow predipitate
Sulphate test
Add hydrochloric acid to remove imputites Add barium chloride White precipitate forms if sulphate ion is present
Carbonate test
Add any acid Should bubble Test bubbles for carbon dioxide
Tests for water
• Anhydrous copper(II) sulphate turns from white to blue • Cobalt chloride from blue to pink
Aqueous cation test
Aqueous sodium hydroxide is added. The colour of the precipitate is observed to identify the cation.
Why does red litmus need to be damp?
Water is needed to form hydroxide ions
Phenolphthalein colours
• Acid / Neutral: colourless • Alkali: pink
Methyl orange
• Acid: Red • Alkali: Yellow